Basic railroad hopper car structures involve an enclosure for holding particulate matter. Such railroad cars are typically provided with a plurality of openings arranged along a bottom thereof. A conventional hopper car is also provided with a series of slope sheets or slanted walls funneling downwardly toward each opening to facilitate the discharge of the particulate matter from the car.
Various methods and devices are known in the art for closing the openings disposed along the bottom of the hopper car. Basically, such closure devices are divisible into two categories. Some hopper cars utilize a sliding gate or valve type device for selectively opening and closing the openings at the bottom of the discharge gate. Alternatively, some hopper cars are provided with pneumatically enabled discharge openings which rely on a pressure differential system for exhausting particulate matter from the enclosure of the hopper car.
A conventional slide gate device includes a frame which is bolted or otherwise secured to the hopper car. The frame defines a discharge opening arranged in operative combination with an opening at the bottom of the slanting walls on the hopper car. A gate is arranged on the frame for sliding movement between open and closed positions relative to a respective discharge opening. When open, the sliding gate permits the contents of the hopper car enclosure to pass gravitationally through the discharge opening defined by the frame of the gate assembly. When closed, the sliding gate shuts off the material or matter flow through the gate.
A conventional pneumatic discharge system for hopper cars involves connecting a discharge assembly including a housing beneath each opening in the bottom of the hopper car. A pneumatic discharge conduit extends from the housing longitudinally of the car and is adapted to be connected to a suction hose or the like for conducting the particulate matter exhausted from the enclosure of the hopper car to any suitable discharge location. An air inlet conduit, connected to a suitable air pressure supply source, introduces pressurized air into the enclosure of the hopper car thereby increasing the pressure therewithin. Preferably, the air is introduced into the enclosure of the hopper car as through permeable sheets typically arranged along the slanted walls of the hopper car thereby promoting movement of the particulate matter toward the openings along the bottom of the hopper car and the particulate matter is withdrawn from the enclosure as a result of the pressure differential.
The transportation and unloading of finely divided materials, and particularly food stuffs, such as sugar, flour and the like within and from the enclosure of a hopper car adds further problems to the design of railroad hopper car discharge gate assemblies. When the lading to be transported involves food stuffs, the FDA has certain rules and regulations which must be met in order for the hopper car to qualify for transporting such food stuffs. Of course, a paramount concern involves designing the hopper car such that no foreign matter, accumulation of moisture, or insect infiltration is permitted to contact and possibly contaminate the food stuffs even while they are being discharged or unloaded from the railway hopper car.
In those hopper cars which transport food stuffs and utilize a sliding gate for controlling the discharge of matter from the enclosure of the hopper car, such gate designs are conventionally equipped with a circumferential housing or skirt depending from the gate in surrounding relation to the discharge opening in the frame of the gate assembly to define a discharge plenum. Typically, an air sled or other portable unload apparatus is clamped to the underside of the skirt during a discharge operation thereby permitting the food stuffs in the enclosure of the hopper car to be discharged directly and protectively into the sled and, thus, conveyed away from the hopper car. To inhibit debris such as dirt, dust, insects, moisture, clay and smoke from contaminating the underside of the gate and the interior of the discharge plenum during transport of the hopper car, such gate designs typically include a sanitary plate or cover which slides between open and closed positions in a horizontal plane generally parallel to the gate to close the discharge plenum during transport of the hopper car.
Sliding gate closures have proven adequate over the years. There are problems, however, inherent with these designs. The frame of the gate assembly on which the gate slides is typically provided with supports or ledges on which the gate moves. Often times there is a buildup of material fines on such ledges following discharge of the particulate matter from the hopper car. When the gate is returned to its closed position, the material fines are deposited on an upper surface of the gate and get in the way of complete sealing of discharge opening on the gate assembly. As will be appreciated, these fines become packed and caught between the surface of the gate and the perimeter of the opening and the gasket or seals that may surround the opening in conventional closure assemblies, thus, preventing complete resealing of the bottom discharge opening of the hopper car.
Another problem has also been identified with sliding gates when the material to be discharged involves fine granular food stuffs or material. As will be appreciated, to enable the sliding gate to operate between positions, an operating gap or opening must be provided between the frame of the gate assembly and the gate. Such gap or opening is typically provided between the skirt on the frame of the opening and the gate. It is through this opening or gap that contaminants, moisture, smoke, dust, clay and insects can enter the discharge plenum, thus, contaminating the food stuffs upon discharge from the hopper car. Moreover, during a discharge procedure, the fine materials from the enclosure of the hopper car leak through even the smallest of openings and are lost thereby causing adverse economic considerations while further complicating the discharge of materials from the hopper car.
Arranging seals or gaskets about the discharge opening in an attempt to close or seal such openings has often resulted in the seal or gasket being pulled from the gate assembly either by the materials exiting from the hopper car or from the sliding movement of the gate toward an open position. Thus, the seals or gaskets often further complicate the discharge of material from the hopper car. Moreover, having fine particulate matter on the top or upper surface of the gate when slid closed further exacerbates the ability of the seals to form an adequate closure relative to the gate of the gate assembly.
As mentioned above, pneumatic unloading devices rely on the creation of a pressure differential to effect unloading of the hopper car enclosure. While this basic concept of unloading eliminates some of the above-mentioned problems of slide gate systems, the pneumatic unloading system increases the complexities of the design of the hopper car as well as the costs and efficiencies as comparted to slide gate unloading systems. By way of example, unloading speed is an important consideration with regard to economical operation and, thus, is an important consideration to some railroads and hopper car builders. Gravity unloading of the various openings along the bottom of the hopper car can be effected substantially simultaneously. Whereas, suction tube or pneumatic unloading through the various pneumatically enabled openings on some hopper cars is limited with respect to number of unloaders available for use with each car. Additionally, pneumatic unloading of a hopper car involves designing the hopper car such that it must hold a gage pressure within the enclosure of up to about 15 psig. when the car is being unloaded. Heretofore known gaskets or seals are simply not capable of holding a pressure of up to about 15 psi. within the enclosure of a hopper car during unloading of the particulate matter from the car.
Thus, there is a need and a desire for a hopper car having an enclosure capable of carrying fine particulate food stuffs therewithin but which is capable of discharging the particulate matter in a manner overcoming the problems identified above.